1. Field of the Invention
The present invention relate to a computer system using a fuel cell assembly as a power supply and, more particularly, to a personal computer using a fuel cell assembly of type which directly oxidizes methanol.
2. Description of the Related Art
Various personal computers using a fuel cell assembly have been devised. In a conventional personal computer using a fuel cell assembly, the fuel cell assembly is set in the personal computer main body.
Such a personal computer is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 9-213359. The fuel cell assembly disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-213359 uses a hydrogen-absorbing metal.
A fuel cell assembly inevitably produces water. This water is normally vaporized using heat generated in the computer. In some cases, however, the vapor liquefies in the housing of the personal computer under various environmental conditions. A design for preventing the water from entering the personal computer conflicts required conditions for heat dissipation, ventilation, and the like.
That is, in the conventional personal computer, the fuel cell assembly is set in the personal computer, and when water produced from the fuel cell assembly enters the personal computer, the personal computer malfunctions.
In addition to a fuel cell assembly with a hydrogen storage unit using a hydrogen-absorbing alloy, a DMFC (Direct Method Fuel Cell) has been devised. Such a DMFC is disclosed in, e.g., Japanese Patent Application No. 10-278759 filed by the present applicant. The DMFC does not require so-called auxiliary equipment for pumping fuel and hence has no movable mechanical portion. For this reason, the DMFC is readily made compact and lightweight and therefore is suitable as a power supply of a notebook personal computer.
If, however, a DMFC is designed not to have a stacked cell structure so as to manufacture the cell at a low cost, air supplied to the cell relies on diffusion and convection. As a consequence, to supply power required for a current notebook PC, the DMFC has an excessively large area. Even if the performance of a DMFC improves to, for example, 45 mW/cm2, the cell needs to have an area of 1,000 cm2 to supply 45 W.
The biggest merit in using a fuel cell assembly for a portable apparatus is that the apparatus can be used substantially unlimited time period in the AC power less embodiment, as long as a fuel is carried. When the fuel cell assembly is used, it is required to restrict a performance and function of the personal computer.
While being out as long as a fuel is carried. However, the power that can be extracted from the fuel cell assembly is limited. If a high priority is to be given to the long-term use of a personal computer even at the expense of performance, the personal computer needs to be operated with a great restriction on power consumption. However, present notebook PCs are not designed to operate on the power that can be extracted from a fuel cell assembly.
Many current notebook personal computers are designed assuming, as a main power supply, an Li ion cell charged using a dedicated AC adapter. In this case, for the viewpoint of efficiency and the like, it is supposed to be optimum to design a secondary cell with a terminal voltage of about 10V by connecting three cells in series in a battery pack.
The cell output voltage of a fuel cell assembly is about 0.5V in operation. A fuel cell assembly having a number of cells stacked (this type is hard to manufacture and be inexpensive) is generally designed to obtain such an output voltage, though it is expensive and difficult to use.
For cost reduction, a personal computer operable by a low-level voltage, which can easily be obtained by segmenting a grid into a plurality of portions in an integrated fuel cell assembly and connecting those portions in series, is necessary.
However, with the low power obtained by such a fuel cell assembly, the conventional computer system cannot normally operate when a power-consuming application is executed.